1. Field of the Invention
The present invention relates to an improved ball lapping machine which performs ball lap machining between two lapping plates, a turn table and a stationary plate.
2. Related Background Art
The conventional ball lapping machine is such that balls are placed between the two lapping plates, rotary and stationary, for lap machining, and is structured in such a manner that only the rotary lapping plate (hereinafter referred to as turn table) is rotatively supported by a shaft while the stationary lapping plate (hereinafter referred to as stationary plate) is connected to the rod of a hydraulic cylinder. As disclosed in Japanese Utility Model Laid-Open Application No. 54-164189, for example, the structure is arranged by providing the turn table 6 and stationary plate 5 oppositely so that the center lines can be horizontal (FIG. 3). In another example, disclosed in Japanese Patent Laid-Open Application No. 47-8599, there each of the lapping plates is arranged oppositely so that the center lines can be vertical (FIG. 4).
In either case, the supply, discharge, and circulation of the balls 7 are performed by a normal method such as shown in FIG. 5.
However, in the conventional ball lapping machines shown in FIG. 3 and FIG. 4, the structures are all arranged to support the turn table 6 and stationary plate 5 from the reverse side of each of the two discs. As a result, these plates are affected by the heat generated in the rotating spindle 42 and the temperature rise of lapping liquid, thus causing the concentricity of the grooves of the respective discs to vary as well as the variation of its parallelism to take place. This creates problems in ball lap machining and reduces the machining precision which results in the degraded sphericity of the finished balls, roughness of finish and the like. Then, the machining load exerted between the discs will also produce similarly adverse effects.
Also, in the embodiment with the horizontal shaft arrangement as shown in FIG. 3, ball stocks 7 are put in the grooves 5a and 6a of both discs at the time of initial setting, but the operation is difficult due to the fine adjustment required for the provision of the space between the discs. In addition, the same difficulty is encountered when the finished balls are drawn after the lap machining is completed. On the other hand, in the embodiment with the vertical shaft arrangement as shown in FIG. 4, there is no operational difficulty such as mentioned above, but abrasive particles and the like are accumulated in the groove of the disc on the lower said to create a problem in that scratches occur on the balls being machined. There is also a problem that it is difficult to circulate the balls smoothly during the lap machining.